1. Field of the Invention
This invention relates to and provides a mechanism for converting a high lift CC (Circulation Control) wing with a rounded trailing edge into a low drag configuration for high speed cruise. The object is to be able to retract and recess the rounded trailing edge in a cavity provided for it at the underside of the wing.
By structurally separating the rounded trailing edge from the flap with its sharp trailing edge, one has the option of employing the flap with or without circulation control.
This structural separation minimizes the drag and associated torque required during the retraction of the blowing air supply duct from the trailing edge position to the cavity at the underside of the wing.
The structural separation allows for thermal expansion of the high temperature blowing air supply duct, without inducing thermal stresses in the flap mechanism.
The junction between the flap and the air supply duct forms an ejector on top of the supply duct which reduces the blowing velocity without lowering the blowing momentum or lift augmentation. It generates suction from the secondary flow in the ejector which cools the flap and provides a suction force between the flap and the air supply duct. 2. Description of Prior Art
The originator of CC high lift generation was I. M. Davidson, who filed British Pat. No. 913754 in 1960, titled "Aerofoil Boundary Layer Control System." The originator of the retractible duct with rounded surface and blowing to get high wing lift was Chaplin, U.S. Pat. No. 3,064,927, Nov. 20, 1962. His actuating linkages and motor were located inside the wing to avoid excessive aerodynamic drag. His patent does not describe the required means to rigidly connect the retractable duct to the wing extremity. The originator of the fully forward folding and retractible flap mechanism was Alberto Alvarez Calderon, U.S. Pat. No. 3,275,265, Sept. 27, 1966. The trailing edge of his flap was rounded by incorporating a blowing air duct at its extremity. Such a configuration with circulation control blowing was first test flown by Loth and Fanucci at West Virginia University on Apr. 10, 1974. The flap was actuated by a hollow actuator arm adjacent to the fuselage with centerline of rotation coinciding with the flap hinge line. This was necessary because the air supply duct is an integral part of the flap as shown by Calderon. This eliminates the freedom in locating the flap hinge point and in operating the flap without blowing. Another draw back of combining the flap and air duct is the large torque required to retract the flap through the 90 degree down position. Various alternate forms of boundary layer control have been proposed. A cascade of blowing slots which increase in number as the flap angle increases, was proposed by Shorr, U.S. Pat. No. 3,974,987 Aug. 17, 1976.
In 1968 the concept of Circulation Control by Blowing over a Rounded Trailing Edge was theoretically investigated by R. J. Kind at Cambridge University. In the following years an elliptical CC airfoil, for helicopter applications, was investigated by R. M. Williams at NSRDC (Naval Ship Research and Development Center), and by R. E. Walters, N. Ness and others at WVU (West Virginia University). In 1970, J. L. Loth at WVU introduced a fixed wing aircraft application of the CC airfoil. The first proposed configuration was the model A wing. This employed a conventional plain flap airfoil of which the structure upstream of the flap hinge was altered. It was modified into a low pressure air supply duct with a slot nozzle allowing air to be blown over the flap. The bottom portion was recessed which permitted the flap to fold under. In this configuration the flap provides a rounded trailing edge for circulation control by blowing. This concept was tested in all three configurations: conventional, blown flap and the CC airfoil mode. The reduction in wing area in the CC configuration prompted the design of the Model B wing in accordance with Calderon's patented configuration. In this design the airfoil fixed sharp trailing edge was equipped with a piano hinge attached to a flap with a rounded trailing edge. In the circulation control configuration the flap was folded out to increase both the wing area and the maximum obtainable lift coefficient. This design was described by Loth at the 1973 SAE Business Aircraft Design Meeting in Wichita, Kans., Paper No. 730328. In 1974 the Model B wing concept was tested at WVU on the first Circulation Control Technology Demonstrator STOL Aircraft. The flight performance test result were reported in the March 1976 issue of the Journal of Aircraft by J. L. Loth, J. B. Fanucci, and S. C. Roberts. A drawback of the model B wing design is that the rounded trailing edge air supply duct is attached to the flap and both must be rotated forward to retract to the cruise configuration. With the flap in the vertical downward position, the associated aircraft drag and required flap torque are large. The second design limitation was that the compressed air supply duct had to exit the fuselage concentric with the hinge line of the flap. The third design limitation was that the flap could not be used independently in the conventional mode, without the rounded trailing edge. These three limitations have been overcome in the improvement presented herein. Soon after the CC concept was flight tested at West Virginia University, the Navy provided an A6 aircraft for modification with a CC high lift device. The CC modification was designed by R. J. Englar at NSRDC as a non-retractable, fixed and large rounded trailing edge. This second CC Technology Demonstrator A6 aircraft was first flown in 1979. The high drag penalty of its fixed rounded trailing edge motivated Englar to optimize CC airfoils with fixed and very small trailing edge radius. This resulted in his 1979 U.S. Pat. No. 4,387,869 on a Combined Supercritical/CCW high lift airfoil. Recent research on CC wing optimization by Loth and M. Boasson is scheduled for publication in the February 1984 issue of the Journal of Aircraft.